For over seven millennia, fermented beverages have been a popular and common drink. Today, wine alone is estimated to contribute over a hundred billion dollars to the American economy. There are more than five thousand wineries in the United States including at least one winery in each state.
Many problems associated with the preparation of alcoholic beverages, including wine and beer, occur during primary fermentation when yeasts anaerobically convert sugar into carbon dioxide and ethyl alcohol by way of the following chemical reaction:C6H12O6(sugar)→2C2H5OH(alcohol)+2CO2(carbon dioxide)
One of the most critical steps required to ensure a successful fermentation is the careful extraction of desirable components including phenols, for example. Phenolic compounds, both natural phenol and polyphenols, include a large group of several hundred chemical compounds that affect the taste, color and mouthfeel of wine. Natural phenols can be broadly separated into two categories: flavonoids and non-flavonoids. The flavonoids include anthocyanin and tannins which contribute to the color and mouthfeel of the wine or other fermented botanical components. The non-flavonoids include the stilbenoids such as resveratrol and phenolic acids such as benzoic, caffeic and cinnamic acids.
High quality (i.e. ultra-premium) wine grapes weigh a mere tenth of an ounce or about one-fifth the weight of common table grapes. The skin to pulp ratio for wine grapes determines the actual concentration of polyphenols. During fermentation, oxygen (O2), hydrogen (H2), and other molecules polymerize new molecular combinations, ultimately imparting an evocative array of complex organoleptic attributes to the finished wine.
The extraction of desirable components can be accomplished via good cap management. Nowhere is this more prophetic than during the production of fine red wine (from grapes) or fruit wine (from other fruit sources), although alcoholic fermentation using any botanical component(s) will undoubtedly benefit from diligent cap management.
Residual sugar (RS) caused by sluggish or stuck fermentations and volatile acidity caused by distillable acids like acetic, lactic, butyric, propionic, and formic acids, are common examples of erroneous ferments; however, the presence of undesirable matter, including chemical and bacterial contaminants, can also be problematic. Most fermentation troubles can be specifically attributed to poor cap management.
On average, about 75 percent of the fermentation activity will occur during primary fermentation. As fermentation proceeds, each yeast cell produces carbon dioxide (CO2) beyond the capacity of the juice to keep it in solution Skins and seeds are less dense than the fermenting liquid and tend to form a solid cap of material which is usually about 33% by volume when fermenting grapes. Carbon dioxide gas bubbles rise and adhere to the solid material causing it to float upward, rise above the juice, and dry out to form a cap as the juice slowly drains away.
Cap Management
Cap management generally relates to the control of physical, chemical and biological interactions between solid cap material (or pomace) and juice (or must) during primary fermentation. The word “pomace” is considered a subset of solid cap material that specifically includes grape skins, grape seeds (i.e. pips) and/or grape stems. The word “marc” refers to only the grape skins and seeds. As used herewith, the word “juice” refers to any liquid component before or during fermentation and the word “must” refers specifically to grape juice before or during fermentation. The word “ferment” refers to any fermenting substance. The word “wine” is generally used to describe the liquid component post-fermentation using grapes. Primary fermentation is used synonymously with alcoholic fermentation and secondary fermentation is used synonymously with malolactic fermentation for purposes of this disclosure and general discussion. The following terms are used interchangeably throughout this document:    aroma/bouquet/essence; mouthfeel/texture/smoothness; and taste/flavor/savor.
The formation of a cap (or chapeau) is a potentially dangerous situation. Left unchecked, the dry cap material, oxygen, and warmth provide an ideal environment for harmful strains of bacteria. If a cap isn't properly managed, several other deleterious events can occur: 1) the cap temperature overheats and kills the yeast before enough sugar is consumed; 2) acetic acid bacteria (e.g. Acetobacter aceti, A. cerevisiae, A. liquefaciens and others) proliferate and begin converting ethanol to acetic acid in the presence of oxygen which, in turn, forms acetaldehyde which ultimately spoils the wine; and 3) the fermentation can stratify and/or stick. A stratified fermentation includes the establishment of two or more distinct micro-environments. This is usually due to insufficient mixing. A stuck fermentation occurs when yeasts become dormant before the fermentation is complete. Poorly managed caps contribute to large quantities of ruined wine each year.
Therefore, it's prudent to manage a fermentation cap to accomplish at least these goals: 1) keep the cap moist enough for the yeast to remain active; 2) keep the cap cool enough for the yeast to remain active; 3) redistribute sugar and nutrients so that they remain accessible to the yeast; 4) keep cap solids in anaerobic conditions to prevent volatile acidity and other issues; and 5) extract desirable components, including phenols.
Historically, a number of enological techniques have been used to accomplish one or more of the above-identified goals. The main categories generally include: 1) pump over; 2) submerged cap; 3) rotary tank; 4) rack and return (i.e. délestage); 5) timed gas-pressure release; 6) pneumatage; and 7) punch down (i.e. pigeage).
Pump over systems remove a volume of juice from the bottom of the vessel and pump it back over the top of the floating cap to keep the cap moist. These systems are one of the more oxidative cap management techniques. Even though carbon dioxide CO2 quickly displaces almost all the oxygen (O2) out of the headspace in the fermentation vessel, the physical motion of the juice falling through the headspace from the irrigator to the top of the cap will tend to cause excessive O2 from the outside atmosphere to be brought into the headspace. Introduction of too much O2 and aggressive mixing are major drawbacks of this approach.
Submerged cap systems use a grate or other partition in the fermentation vessel to keep the skins submerged throughout the fermentation. Unfortunately, this type of cap management system often causes stratification unless a pump over system is also employed.
Rotary tanks are rotated on their horizontal axis which leads to mixing the pomace (i.e. grape skins, seeds and stems) with the must (i.e. grape juice) during winemaking. This assures regular contact of the cap and ethanol produced by the yeasts and also creates a more uniform temperature during the fermentation. Stationary mixing tanks provide a vertical impeller for mixing. These types of systems allow for maximum extraction in a minimum amount of time. This is not necessarily an advantage because aggressive mixing often results in an imbalance of tannin and fruit and/or excessive oxygenation which can age wine prematurely. In fact, with the exception of Sherry, Port, Madeira and white wines from the Jura region of France, oxidation is considered a technical fault. Wines lacking the protective benefits of tannins are more susceptible to oxygen exposure during the winemaking process.
Rack and return (délestage) is a common cap management protocol used in winemaking that first removes of all the must from the fermentation vessel. The must is then poured back onto the cap to fully submerse the cap. When used with ripe fruit, this regime can lead to a wine with less structure. Therefore, this approach should be reserved for wines showing excessive tannins.
Timed gas-pressure and release systems, including those produced by Ganimede®, capture CO2 as it is produced during fermentation. The gas displaces some of the must and lifts it upward in the fermentation vessel. A solenoid periodically releases the gas to allow the cap to fall back in the vessel. This action is designed to break up and irrigate the cap.
Pneumatage employs plates to trap gas bubbles until the resulting bubble is large enough to overcome the surface tension of the liquid at which point the growing bubble escapes from under the plate and ascends through the must. The movement of the bubble through the column of must breaks up the cap when it reaches the surface. Pneumatage, as well as the previously described gas-pressure and release systems, are not economical methods for small (i.e. boutique) wineries and it's sometimes difficult to control the mixing as the bubbles randomly ascend.
The term “punch down” (i.e. pigeage) describes the process of breaking up the cap by randomly pushing it back down into the juice. While pigeage doesn't require any pumping, it aggressively mixes the cap by disintegrating the cap material to disassociate the pulverized cap material into the juice. Pigeage is also somewhat limited by the size of the fermentation vessel. Fermenters larger than five tons tend to generate caps that are too thick for manual pigeage and thus benefit from a semi-automatic system. Fully-automated industrial pigeage systems can get as large as 35 to 50 tons in capacity.
Regardless of the mixing technique or fermentation vessel chosen, the duration of time the solid components are in contact with the juice is the controlling factor for extraction of phenolic compounds. Excessive extraction and the accompanying bitterness and astringency that follow can cause yet another set of problems. Red wines are typically aged longer than white wines so excessive extraction may be tempered by extended aging of red wines, in particular. However, additional aging may not be an option due to controlling economic factors or limited long term storage capacity, for example.
Extraction can be difficult to control. Microwave irradiation and thermovinification are two extraction techniques that have been used. Thermovinification heats up the entire cap material. This method favors extractions but can reduce the desirable characteristics and compromises color stabilization to ultimately lower the quality of the finished wine. Irradiation can be expensive to implement and may destroy a large amount of important phytochemicals and nutrients.
Traditional pigeage tools, such as the example shown in FIG. 1, can cause seeds to be inadvertently crushed between the disk and the bottom of the vessel which exacerbates the release of harsh tannins into the wine. This is a particular concern when using shallow open top fermentation vessels. Conventional tools are also difficult to push downward and lift upward due to the lack of hydrodynamic design and the strong resistance created by the disk as it is moved through viscous juice. The solid components also adhere to the top of the disk making it difficult to lift the tool out of the vessel and move it to other locations around the fermentation vessel when mixing the components. Solid components are sometimes dislodged from the disk by banging the tool on the edge of the vessel. This can be messy and unsanitary as must and/or pomace randomly splatter.
Manual cap punch down requires significant strength and can cause back pain and physical injury, particularly if the worker is standing alongside the fermentation vessel and must lean over the vessel to punch down the cap. Alternatively, punching down a cap may require balancing on the edge of a fermentation vessel or catwalk to position the worker directly above the vessel. In these days of health and safety awareness it is somewhat surprising that this operation is still permitted, as a number of people have fallen into vessels of fermenting wine while punching down the cap, several with fatal results.
Automated punch down units have eliminated the physical strength required during pigeage and are routinely used in industrial bulk wine production; however, the expense and maintenance of specialized machinery eliminates automation as a viable option for boutique commercial wineries and hobbyists. Furthermore, automation of traditional mixing techniques does not solve other cap management issues such as mitigating reduced sulfur compounds, harmful bacteria, multicellular fungi and/or biogenic amines. Nevertheless, some embodiments of the invention are suitable for automated punch down units, commercial wineries, or wherever cap management can be improved.
Reduced Sulfur Compounds
Sulfur (S) is difficult to avoid during fermentation because relatively small amounts are naturally present on many fruits. Larger amounts of sulfur may arrive on harvested grapes sprayed in the vineyard to protect the crop from disease. The chemically related sulfites are reported by some consumers to be a significant cause of headaches and perhaps other maladies. Small amounts (about 10 parts per million) of hydrogen sulfide (H2S) and other reduced sulfur compounds are formed when yeasts convert sulfur to H2S during fermentation in an oxidation-reduction reaction as shown below with net electron transfer indicated:S0(sulfur)+H20(hydrogen)→S2−H2+(hydrogen sulfide)
Hydrogen sulfide formation is a chronic problem in the wine industry worldwide. Under normal conditions, some H2S is volatilized from the wine or other ferment along with CO2; however, the residual H2S may pose a serious problem due to its low sensory threshold and its potential reactivity. Hydrogen sulfide smells of rotten eggs and is generally considered to be a fatal flaw in finished wine. Amounts of H2S over 1.0 parts per billion (ppb) are readily detectable by human olfaction. Even amounts below this threshold can react with ethanol or acetaldehyde to form mono- and di-mercaptans, which radiate strong garlic and petroleum aromas, respectively, both before and/or after bottling as generally depicted below:H2S(volatile)→mono-mercaptans(becoming bound)→poly-mercaptans(bound)
Removal of H2S, particularly bound mercaptans produced near the end of fermentation, can be extremely difficult if not technically challenging. This process is not discrete. While H2S is present, it is likely that mono-mercaptans are forming; and poly-mercaptans may be forming before the H2S in its volatile form disappears. Research shows that mercaptan formation occurs within a few days after the beginning of fermentation and is at its peak at about two months after which the poly-mercaptans become dominant.
One traditional “solution” used to eliminate H2S has included aeration; however, mono- and di-mercaptans are formed by aggressive aeration. Therefore, aeration may actually compound the problem or at least require subsequent protocols to remove the mercaptans. Even gently splashing wine to eliminate sulfide aromas can encourage the formation of disulfides which can serve as a reservoir from which sulfides can be re-formed under reductive conditions such as after bottling.
In more severe or advanced cases, solutions of, or filters impregnated with, copper sulfate (CuSO4), have been used to remove H2S and mono-mercaptans. However, copper sulfate is poisonous and, therefore, requires further steps of fining with bentonite (or another absorbent aluminum phyllosilicate) or Sparkolloid® in order to remove it from the ferment. The fining agent must then be removed by filtering which, unfortunately, also removes many of the desirable components of the wine. Other methods use radiation to remove harmful gasses from wine but this approach prematurely ages the wine and is expensive to employ in small scale winemaking operations.
Another way to manage cap micro-environments and prevent reduced sulfur compounds includes using yeasts that are genetically modified not to catalyze the conversion of sulfite to sulfide. However, the use of altered organisms remains controversial and this approach does nothing to address control of reduced sulfur compounds in non-inoculated fermentations (e.g. using only wild or natural yeasts), for example.
Harmful Bacteria
Harmful bacteria are another potential inhabitant of the cap and surrounding material. Although some forms of lactic acid bacteria (principally Oenococcus oeni) play a positive role during malolactic fermentation (MLF), bacteria can prove detrimental during primary fermentation, particularly if the pH rises above about 3-4 as this range encourages bacterial proliferation. Most recalcitrant bacteria belong to the genera: Leuconostoc (rancid butter flavor); Pediococcus (bitter flavor); and Lactobacillus (sauerkraut aroma). These organisms are gram positive and can grow well throughout various depths in the ferment because they are microerophilic (i.e. they do not require much oxygen). Both lactic acid bacteria (LAB) and acetic acid bacteria (AAB) routinely exist on the surface of grapes prior to crushing. The subsequent crushing process increases the propagation and colonization potentials of these microbes. In addition, harmful bacteria can also contaminate the grape juice via winemaking equipment and spoilage biofilms formed inside hoses and pipes. Some species or strains of lactic acid bacteria acidify wine and give it an undesirable bitter palate and/or musty odor. Harmful lactic acid bacteria can also form biogenic amines in the wine. Acetic acid bacteria can spoil wine by literally turning it into vinegar.
If harmful bacterial cells are identified early, their numbers may be kept to a safe level. Attempts to control harmful bacteria have included, for example, treatment with sulfur dioxide (SO2) gas, potassium metabisulphite (K2S2O5) and/or filtration. As previously discussed, adding forms of sulfur and/or filtering have their own unique drawbacks. Potassium metabisulphite is also an allergen for some individuals.
Multicellular Fungi
Multicellular fungi may also find a suitable home in cap material, especially when spores are inadvertently transferred into the winery from the vineyard during harvest. Mold and mildew are two common examples of fungi that can spoil wine or other liquids during primary fermentation. Spores of mold and mildew, like bacteria and yeasts, naturally exist on most surfaces. Too much head space in a covered fermentation vessel or tank or unsanitary equipment contribute to their growth and potential ecological succession. A musty odor, wet wood odor, or an oily/rainbow appearance on the surface of the liquid are usually initial indications of a fungus problem.
A common “solution” in wine tainted by mold and/or mildew is to rack the wine into a sanitized container. This step is followed by the addition of campden tablets to remove the additional oxygen introduced by racking Campden tablets are a sulfur-based product, usually in the form of sodium metabisulfite, that suffer from the same limitations as previously described.
Biogenic Amines
Biogenic amines can be formed by a wide range of yeasts and some (mostly malolactic) bacteria. Most important among the amines found in wine are histamine and tyramine. The presence of histamine, like sulfites, has been implicated as a potential cause of headaches that some people experience after imbibing alcoholic beverages. Biogenic amines may cause allergic reactions and changes in blood pressure as well. Other biogenic amines such as cadaverine and putrescine, as their names suggest, have extremely foul odors which mask fruit flavors (and turn stomachs). Preventive techniques include cold soaking combined with flash pasteurization. Curative reduction of biogenic amines by bentonite absorption and yeast cell hull preparations have been attempted albeit with mixed results. Separation columns or filters have been used but these methods fail to adequately select only the undesirable matter and, therefore, inevitably also remove attributes which make a positive contribution to the quality of the wine.
Information related to attempts to address these problems can be found in U.S. Pat. Nos. 4,473,001; 4,479,721; 4,745,068; 4,474,890; 4,934,828; 5,472,278; 5,744,183; 5,972,402; 6,125,736; 6,703,055 B1; 6,905,601 B2; 7,198,809 B2; 7,353,750 B2; 7,571,673 B2; 8,216,803 B2; and United States Patent Application Publication Numbers: 2005/0147776 A1; 2006/0156929 A1; 2006/0240146 A1; 2008/0175951 A1; 2010/0143536 A1; 2011/0024418 A1; 2011/0305794 A1; 2012/0064610 A1; 2012/0190386 A1; and 2012/0269925 A1 as well as European Patent Numbers: EP 0089225 A2; EP 0871699 B1; EP 1049764 B1 and International Patent Publication Numbers: PCT/WO 97/14781 A1; and PCT/WO 03/011440 A1, for example. Various types of cap management equipment and technologies, including some embodiments of the invention, can mitigate or reduce the effect of, or even take advantage of, some or all of these potential problems.
For the foregoing reasons, there's a legitimate need for effective and efficient ways to facilitate cap management including selectively mitigating undesirable matter during fermentation. It would be particularly beneficial and desirable to provide methods and apparatus for cap management to facilitate some or all of the following: regulate fermentation parameters; optimize organoleptic attributes; and/or selectively and simultaneously mitigate (or eliminate) undesirable matter including reduced sulfur compounds, harmful bacteria, multicellular fungi and/or biogenic amines.